1. Field of the Invention
The present invention relates to a radio transceiver whose output level is specified by a base station, for example, and which transmits a transmitting signal at a specified output level to the base station or other destination.
2. Description of the Prior Art
FIG. 1 is a block diagram showing a transmitting output control section for an automobile telephone set of a conventional type. In the figure, 10 is a transmitting signal input terminal at which a transmitting signal is to be received; 11 is an amplifier for amplifying the transmitting signal; 12 is a detector (transmitting power detecting means) which detects the level of an output signal of the amplifier 11; 13 is an automatic power control comparator (hereinafter referred to as APC comparator) which constitutes a transmitting power control means in which a DC voltage output by the detector 12 and an output of a voltage generator,14, to be explained later, are compared; the voltage generator 14 (transmitting power control means) outputs a reference voltage based on a selection signal 152; 15 is a control section which develops selection signal 152 converted from the level information to the voltage generator 14; 16 is a receiving section which demodulates an input signal; 17 is an antenna multicoupler which supplies an amplified transmitting signal from the detector 12 to an antenna input-output terminal 22 and also supplies a received signal from the antenna input-output terminal 22 to the receiving section 16.
The operation is explained in the following. An input signal sent out from a base station or the like (hereinafter referred to as simply a base station) is inputted to the input-output terminal 22 and through the antenna multicoupler 17 to the receiving section 16. The input to the input-output terminal 22 may be from a separate antenna 22a.
The receiving section 16 demodulates the input signal and outputs transmitting output level information (hereinafter referred to as level information) to the control section 15. The level information which is contained in a demodulated signal specifies the output level of the transmitting signal (transmitting output level).
The control section 15 develops a selection signal 152 from the level information and outputs signal 152 to the voltage generator 14. The selection signal 152 differs from the level information only in the data format, otherwise containing substantially the same information.
The transmitting signal is inputted to the transmitting signal input terminal 10, amplified by the amplifier 11 and supplied to the antenna 22a through the detector 12, the antenna multicoupler 17 and the antenna input-output terminal 22. The detector 12 detects an amplified transmitting signal level and generates a DC voltage corresponding to the transmitting output level. The signal passes through filter capacitor 12a and charges capacitor 12d according to the RC time constant determined by resistor 12c. A diode 12b is provided to prevent negative components of the AC signal from amplifier 11 from affecting the charging of the capacitor 12d. The voltage generator 14 generates a specified voltage corresponding to the output level specified by the base station as represented by selection signal 152. The APC comparator 13 compares the DC voltage and the specified voltage and adjusts the amplification factor (gain) of the amplifier 11 so that both voltages are in balance.
FIG. 2 is a circuit diagram showing detailed configurations of the detector 12, the APC comparator 13, the voltage generator 14 and the control section 15. The component parts in the figure are explained as follows. 131 is an operational amplifier for changing the amplification factor of the amplifier 12; 132 is a feedback resistor; 133 and 134 are transistors for amplifying the output of the operational amplifier 131; 141 is a selector for selecting one of the resistors 143x to 143z; 151 is a selection signal setter which receives the level information from the receiving section 16 and converts it to a selection signal for selecting a corresponding resistor among the resistors 143x to 143z; 144 is a resistor which is used together with resistors 143x to 143z, for setting a reference voltage 145 which is connected to a non-inversion input terminal of the operational amplifier 131.
Next the operation will be explained. The values of the resistors 143x to 143z, resistor 144 and a feedback resistor 132 are so selected that the amplification factor of the amplifier 11 can be set to correspond to each of the plural levels dictated by the level information. In this state, the selection signal setter 151 outputs a selection signal 152 for selecting one of the resistors 132x to 143z which develops a reference voltage proportional to the amplification factor corresponding to the level information received from the receiving section 16. The selector 141 selects one of the resistors 143x to 143z based on the selection signal 152. If the resistor 143x, for example, is selected, a generated voltage divided by the ratio between the resistor 144 and the resistor 143x becomes the output reference voltage of the voltage generator 14. The operational amplifier 131 produces an output signal which, through feedback connection of resistor 132, changes the amplification factor of amplifier 11 until the input voltage at the inversion input terminal, that is, the voltage output by detector 12, is equal to the reference voltage, and the amplification factor of the amplifier 11 is determined based on the output signal of operational amplifier 131. When level information designating a different transmitting output level is input, a selection signal 152 for selecting another resistor 143y or 143z is output to the selection signal setter 151.
In this way, an amplification factor corresponding to one of these plural levels of the level information is selected, and a transmitting output level is determined by controlling the gain of amplifier 11 as designated by the level information. The number of levels of the level information is assumed to be three to simplify the explanation; that is, the number of steps of the output voltage of the voltage generator 14 is assumed to be three but actually the proper number of steps corresponding to the system requirements will be used.
FIG. 3 shows an example of discharge characteristics of a battery which can be used for this transceiver. In the figure, "C" means the battery capacity in ampere-hours and a discharge rate of 1C represents a discharge current flow that will discharge the battery in one hour. When the current consumption is 2C, the usable time duration of the battery becomes about half in comparison with the case where the current consumption is 1C.
The conventional types of transceivers are constituted as mentioned above; therefore, even if each level has an allowable tolerance range for the reference value, the transmitting output at each level is a fixed level corresponding to the level information, and an increase or decrease in the transmitting output level is not possible, so that lowering the power consumption or raising the transmitting output level in the range of tolerance when the noise level is high is not possible. These have been problems in the conventional prior art equipment. Similar prior art is described in Japanese laid-open Patent Application No. 97020/88.